Evaluation of the Role of Radiation Therapy in the Management of Malignant Thymoma

Abstract

The management of patients diagnosed with thymoma remains unclear. This report attempts to identify the impact of adjuvant radiotherapy on overall survival (OS) and cause-specific survival (CSS) in patients diagnosed with thymoma. Patients diagnosed with thymic malignancy between 1973 and 2003 were retrospectively identified from centers participating in the Surveillance, Epidemiology, and End Results (SEER) program. Those patients classified as having thymic carcinoma were excluded from this analysis. OS and CSS were estimated by the Kaplan-Meier method. Outcomes for patients treated with and without radiation therapy were compared using the log-rank test. Multivariate analysis was performed with the Cox proportional hazards model to analyze factors predictive of OS and CSS. A total of 1,464 patients were identified as having thymic malignancy, and of these, 1,254 patients were identified as having malignant thymoma. The median follow-up time was 41 months (range, 4-337 months). Among patients who did not receive radiotherapy (RT), the 10-year rate of OS was 41% compared to 42% for those who did receive RT (p = 0.06). The median OS for the patients who did not receive RT was 80 months compared to 97 months for those who did receive RT. In patients with Masaoka stage II-III malignancy, OS was significantly improved with RT (p = 0.002), and a trend in improved CSS was observed (p = 0.1). Patients were also analyzed based on resection status. For those patients who had an incomplete excision, the 10-year OS was 63% with RT and 46% without RT (p = 0.38). On multivariate analysis, factors predictive of OS included age, extent of surgery, stage, and number of lymph nodes examined. This study reports treatment results of a large cohort of patients who were diagnosed with malignant thymoma. This study demonstrates that the use of RT following resection for thymoma significantly improves OS for those with regional disease and marginally improves CSS.